The invention relates to the field of very-high-density memory device that utilizes a scintillating medium for data storage.
With the development of the internet, the desire for video-on-demand services, and increases in high-volume-data applications, the demand for high-density memory will continue to grow. Currently, there are two prevalent types of high-density data storage media. One is based on magnetic storage and the other is termed optical-data storage. For commercial magnetic-storage media, data-storage densities of about 2 billion bits per square centimeter (2 Gb/cm.sup.2) have been achieved. Data storage densities of about 100 Mb/cm.sup.2 have been achieved for commercial optical data storage. It is desirable to obtain even higher memory-storage densities.
Both magnetic-storage and optical-storage techniques incur significant technical difficulties as the data-storage density is increased. For magnetic storage, increasing densities imply a smaller size for the individual magnetic bit, and this reduction in size leads to a decreasing magnetic field. The data-reading head must then be moved closer to the disk to detect the bit. Presently, the magnetic reading head rides on a cushion of air and floats much less than 1 micron above the disk surface. As the bits are placed closer to each other, they are likely to interact and spontaneously flip the magnetic field from bit to bit, ruining the stored data.
Optical-data storage suffers from a similar problem of data readability. For CD-ROM, the bit size cannot be made significantly smaller than the probing size of the focused optical field at the substrate. This probe size is on the order of 1 micron for laser diodes and inexpensive optical lenses. Novel near-field optical reading schemes have been proposed (see Martin et al., Appl. Phys. Lett., Vol. 7 (1997)), but the reading head must be brought to within 0.01 microns from the surface to detect the bit. Any particles on the storage-medium's surface could irreversibly damage the reading head for both optical-and magnetic-storage schemes. It is desirable to locate the data-reading head several millimeters from the storage-medium's surface.
A related problem for magnetic- and optical-data-storage devices pertains to the quality of the signal derived from the stored data, i.e., how well can a "low" data bit be distinguished from a "high" data bit. As the bit size decreases, the signal level from the data bit decreases while system noise remains unchanged. The resulting noisy signals for magnetic- and optical-data-storage devices are likely to cause data read-out errors.
Another problem that will be incurred by very-high-density magnetic and optical-data-storage devices is an inability to follow the data tracks precisely on the data-storage medium. As the data tracks are packed closer together, the reading head must be able to navigate directly along the data track, which may be deviated. It is likely that the massive reading heads for magnetic- and optical-data-storage devices will "jump" data tracks, since they cannot be deflected easily at high speeds to follow the data path. It is desirable to provide a means for precisely following the data tracks at high speeds or read-out rates.